1. Field of the Invention
The present invention relates generally to mechanisms for inserting and extracting circuit boards from system rack assemblies. More particularly, this invention relates to an improved mechanism for inserting and extracting circuit boards in applications where large insertion forces may be required.
2. Description of the Relevant Art
Electronic systems such as computers are typically constructed in a modular fashion from circuit boards, each circuit board generally performing a specific function. Each circuit board requires multiple electrical connections which are generally provided by two part multi-contact electrical connectors which include a board part of the connector attached to the circuit board and a second part attached to a rack, system chassis assembly, or another circuit board (e.g., backplane circuit board), which acts as a socket for receiving the board part of the connector. As used herein, “circuit board” generally means any assembly or structure that contains electrical components (including, but not limited to, semiconductor devices, resistors, capacitors, relays, switches, and connectors) or electrical connections for an electrical system. “Circuit board” includes, but is not limited to, a fibreglass printed circuit board. As used herein, “rack” or “rack assembly” generally means any assembly or structure adapted to receive a circuit board, including, but not limited to, a rack, system chassis assembly, or backplane circuit board. Successful mating of the connector parts is required in order to provide reliable electrical connection between the first and the second parts of the connectors.
A number of mechanisms are known for inserting a circuit board into a rack assembly or extracting a circuit board from a rack assembly. Such mechanisms may comprise a lever arm pivotally coupled to the circuit board and arranged to engage a projection formed on the rack. Guide formations may be provided on the rack to receive the circuit board and to guide the circuit board into a load position in which the board and rack parts of the electrical connector engage. The lever arm may be arranged on the circuit board so that when the lever arm is in a raised position, the connector and socket are disengaged, whereas when the lever arm is lowered by application of force, the circuit board is provided with a biasing force that serves to move the circuit board in a direction guided by the guiding formations towards the socket, thereby mating the first and second parts of the electrical connector.
For circuit boards with connectors having a relatively large number of pins, large insertion forces may be required to engage the connectors. For example, a large board may contain twenty or more multi-contact connectors that contain several thousand individual contacts in the aggregate. Each contact requires the application of an insertion force to seat the contact. Thus, the total insertion force required to seat a large board may be 500 pounds or more. Moreover, individual contacts are easily damaged if the mating connector parts are not properly aligned when they come into contact with each other. This problem is especially acute where large forces are required to mate the connectors.
Circuit boards may encounter a variety of external loads. Some loads relate to environmental conditions while in service, such as shock or vibration. Other loads are encountered during assembly, such as those applied during installation or removal of components on the circuit board or other elements in the rack assembly. In either case, the loads may cause separation of or damage to individual contacts, resulting in reduced reliability of the system. Special purpose hardware, such as screws, bolts, or clamps, may be used to contain the circuit board in view of such loads. However, the use of such hardware increases the complexity and cost of the system.
Accordingly, there is a need for an improved mechanism for inserting and extracting a circuit board that enables application of a large insertion force and facilitates successful mating of connector parts without damage to the contacts. There is further a need for an improved mechanism for maintaining a circuit board in place when the circuit board encounters external loads.